Question

A body floats in a liquid contained in a beaker. The whole system as shown in the figure falls freely under gravity. The upthrust on the body is

• A. zero
• B. Equal to the weight of the liquid displaced
• C. Equal to the weight of the body in air
• D. Equal to the weight of the immersed portion of the body

Answer 1

The correct option is A zero

We know upthrust $=V_{\rho} g_{effective}\\g_{effective}=(g-a) a=acceleration downwards$

When body is freely falling,

$a=g{g}_{effective}=(g-g)=0Upthrust=V_{\rho }\times \left(0\right)=0$

So, upthrust on a freely falling body is zero.